9p: remove unused code in 9p

These codes have been commented out since 2007 and lay in kernel
since then. So, it's better to remove them.

Link: http://lkml.kernel.org/r/20200628074337.45895-1-jianyong.wu@arm.com


Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>